X-ray timer



11, 1945. M. M. SCHWARZSCHILD 2,334,647

'x-RAY TIMER Filed Jan. 30, 1943 2 Sheets-Sheet vl m N i 1 II Il II I E! L.

" 4 Fig.1

' Myron M. SchwarzschiId INVENTOR.

ATTORNEY Sept. 11, 1945. M. SCHWARZSCHILD 2,384,647

x-Ru TIMER 2 Sheets-sheaf. 2

Filed Jan. 30, 1943 m m c 5 Z r a W h c M. n m V; M,

v E N m T T 4 Patented Sept. 11, 1945 STATES PATENT or FlCE: I 2,384,647

,tlfii fifiiiflii;333321222729 8- Claims. (Cl. 250-95) The: present: invention nelateslto apparatus for thetiming of Ila-ray exposures I A: satisfactory radiograplm is: the result oi the application of. the proper combination oi electrical. quantities to. the. X-ray tube for the proper time The current through the X-ray tube; which: is determined principally by the temperatureot. the filamentary cathode, has a reciprocal relation to the time of exposure. Thus atia-given voltage, an exposure for onesocond withaicun'ent oi 100 milliamperes is equivalent to an exposure for. twoseconds with a current t 50 milliampores It is thus apparent. that the product of current and,- time isthe determining factor. quantity repcesents the total charge passing thro h the; tube; and istusually expressed in mil.- hampers-secondunits, one milliampere second being? the thousandth part or the electrical unit 0% charge the. coulomb;

The common method of making an X-ray exposure involves the predetennination: of the tube current-by'adjustment cat the filament current and the predeterminiatiom oi the exposure time by means of a timer operated by some form of constant speed. motor or: other device which fixes the duration of the exposure: in terms of time; Each of theserquanti ties, current and. time,v are thus set separately although it is thesingleproduct-whichaisof significance;

It: is; therefore, an: bject of: this invention to provide accurate and dependable means tapermi't thepredetermined setting, of the total quantity of electric cha'rgewhich it is desired topass through the X-ray tube during the exposure. in one" operation, without accurate andior' independent setting. of; the filamentcurrent and. the

tlfll;

It isa further object or thisinventicn: to. provide an accurate andidependable means to permit the predbterminedxseiiting or the total electric charge which what pass through the X-ray tube during the exposure without this total; bein v a'ftested by any fluctuations in the filament term perature oi the X-ray tube such as are likely to be encountereddu'ring an exposure.

Attempts have been mam the past taprovide a milliampere-eecoudatimer, butso far as the applicant is aware; such deviceshave always suffered from a lack (Ii-accuracy and dependability.

It is another object of this invention to provide a device? whiciimaxy be attachedto exist mg X-ray machines and equipment or incorporated in the design of such machines or equipmentin the future and which shall permit accurate exposureihidependent of even large fluctuations in: line voltage.

Another feature of this invention is that it provides an accurate and dependable milliampere-scconds timer which may be so constructed that failure of any of. its tubes will not; result, in a lengthening of'the) exposure with possible disastrous effects, such as damage to the expensive X-ray tube.

These and; other incidental ends andobject's of the invention will hereinafter appear in the prog ress of the disclosure and as pointed; out in the appended'cl'aims.

Accompanying, this specification are drawings showing the. manner ofl operation of'the invention and a preferred embodiment thereof,, wherein:

Figure 1 illustrates thev basic principle of. the invention, this. figure being. introduced only in explanation,

Figure 2 illustrates a modification, which con verts the basic scheme shown in Figure I into. a. practical device; figure being. also introduced to explain the operation of. the ihvention, and' Figure, 3 illu t ates practical and preferred embodimentof this invention. v

Referring, particularly to Fig. 1', numeralv l' designates an A.. C.. power line which supplies filament, 2 of an XY-ray tube 3 through a, transformer 4' and the. primary 5 of, a high-tension transformer 6 through the normally open contact 1 at a. relay 8.. The coil" a of, relay 8 issupplied from the line I through the normally open con.-

v tact H! of a push-button H and the normally closed contact I2 oi alrelay [3.

Secondary coils l4 and I5 of the high-tension transformer 6 supply the X-ray tube 3, one terminal I6 of coil l5 being'cornnectedto oneterminal' of the filament 2, the other terminal H of coil [5 being earthed'. One' terminal I! 01' coil 14 is connected. to anode I9, the other terminal 211' of coil l4 being connected to one terminal of condenser 2f, the capacity of which may be varied. The. other terminal 01' condenser H is earthed. Tube 22' is a control tube which may be a gas" diode. The anode 23 of tube 22 is connected to earth through the coil 24 of relay I3"; while the cathode 25 of this tube 22 is connected to the unearthed terminal of condenser It.

When the push-button H is opera-ted contact 1 closes and the generation of X-rays begins. The flow of charge through the X-ray tube 3 causes the condenser II to become charged to a voltage depending. at any instant upon the number of miIliampere-secondswhich have flowed through tube 3 and upon the capacity of condenser 2|. Gas diode 22 has the propertyot becoming. conductin when the difference of potential' between its electrodes attains a certain deflnite value, the ignition voltage of the particular tube used, When that amount-of charge has traversed the X-ray tube 3' and charged the condenser which is required to cause the condenser voltage to equal the ignition voltage, tube 22 becomes conducting; it is' said to ignite. "Relay [3 now operates opening; the circuit of coll 9 of relay 8. The consequent opening of contact 1 terminates the X-ray exposure.

The most fundamental practical difficulty with the simple circuit of Fig. 1 lies in the very large value of capacity required for the condenser 2| for values of milliampere-seconds and ignition voltage likely to be encountered. If C is the capacity in microfarads, E the ignition voltage and Q the charge in milliampere-seconds, then Exposures requiring 300 milliampere-seconds are not at all uncommon and a value of E of 200 volts is reasonable. These values lead to a figure of 1500 microfarads for the capacity of condenser 2|. A condenser of good constancy of this size to operate at 200 volts is unwieldy, heavy and very expensive.

An object of this invention is to provide a means for accomplishing the desired result with the use of condensers of reasonable capacity.

Fig. 2 illustrates how this last object is attained. The circuit shown in Fig. 2 is the same as that of Fig. 1 except that condenser 2| is now charged through a rectifier 26 from a centertapped secondary 21 of a low-tension transformer 28 the primary 29 of which is in the secondary circuit of the high-tension transformer 6. Transformer 28 may also be used with an untapped secondary but more rectifiers would then be required, as is clear to anyone skilled in the art.

If theinductance of winding 21 is sufficiently great the charge delivered to condenser 2| bears a definite ratio to the charge which has traversed the X-ray tube 3. This ratio is app at y equal to theturns ratio of the transformer 28 if this transformer is constructed with a high coefficient of coupling. If the turns ratio is 1 (number of primary turns+number of turns in each half of the secondary winding) and k is the coefficient of coupling between the primary and either half of the secondary, then Obviously, by suitable choice of k and r, C may be brought within a practical range.

The secondary winding 21 must be of a sufficient number of turns in relation to the core size and material so that the inductance of each half of this winding is greater than l000E/4krfI circuit required for such connection are obvious 1 to anyone skilled in the art and have no important bearing on the working of the invention.

Terminals l6 and ll! of the high-tension windings l4 and |5 may be connected directly to the X-ray tube 3 as in Figs. 1 and 2. Such would be the case in the self-rectified or half-wave rectifier generators, except that in the latter the earthed terminal l1 of coil l5 would not be earthed directly but through a valve tube. In the case of full-wave rectifier systems of the conventional type terminals l6 and [8 would be con- This circuit is drawn with the line nected to two terminals of a four valve bridge, the other two terminals of which are connected to the X-ray tube.

The secondary current in the high-tension winding |4 passes to ground through primary winding 29a of transformer 28a. Coil 28a may be a tapped coil, as shown, in which case the inductance of the secondary winding 21a is determined in accordance with the smallest number of primary turns to be used. The coupling of transformer 28a may be adjustable, for example, by winding the primary upon an armature which may be adjusted in angle. If the coupling is adjustable the inductance of the secondary winding 21a must be determined in accordance with the minimum value of the coupling coeflicient. The condenser 2|a may be arranged as a bank of condensers with a tap switch 30 for selection of the'desired value of the capacity. Secondary winding 21a is shown as a center-tapped coil to feed condenser 2|a through the single rectifier 26, each end of coil 21a being connected to one of the plates or anodes 3| and 32 of tube 26. The filament 33 of tube 26 is supplied by secondary 34 of heating transformer 35.

Tap 30 of condenser 2|a is connected to the midpoint of coil 21a and to one end of resistance 36 and to anode 12 of voltage regulator tube 60. The other end of resistance 36 is connected through the normally closed contact 38 of pushbutton 39 to the positive terminal of condenser 2|a which terminal is also connected to the midpoint of filament transformer secondary 34, to one end of coil 40 of relay 4| and to the midpoint of secondary 42 of transformer 43, which feeds the filaments 44 and 45 of amplifier tubes 46 and 41. The anodes 48 and 49 of these tubes are'connected respectively to the ends of the secondary winding 50 of transformer 5|. The midpoint of coil 50 is connected through the normally open contact 52 of relay 4| to one end of coil 40. Contact 52 is shunted by normally closed contact 53 of push-button 39.

The positive terminal of condenser 2|a is also connected through resistance 54 to the anode 55 of control tube 22a and to the grids 56 and 51 of tubes 46 and 41. The cathode 56 of tube 22a is connected to the adjustable tap of potentiometer 31. One end of potentiometer 31 is connected to the anode 12 of tube 60 through resistance 59. The cathode 6| of tube 60 is connected through resistance 62 to the other end of potentiometer 31 and through resistance 63 to one terminal of a condenser 64. The latter terminal is also connected to the midpoint of winding 65 of transformer 5|. The other terminal of condenser 64 is connected to the midpoint of winding 66 of transformer 61 which supplies the filament 68 of rectifier tube 69 and is also connected through the coil 10 of relay 1| to the anode 12 of tube 60. The plates or anodes 13 and 14 of rectifier 69 are connected respectively to the ends of winding 65 of transformer 5|.

Transformer secondary 65, tubes 60 and 69, transformer 61, condenser 64 and resistances 59, 62 and 63 constitute a regulated power supply system feeding the control potentiometer 31.

The normally open contact 15 of push-button 39, the normally open contact 16 of relay 4| and the normally open contact 11 of relay 1| are all connected in series with the line and the coil 9 of relay 8. The contact 1 of relay 8 controls the circuit of the primary 5 of the high-tension transformer 6. The primary 18 of transformer 5| is connected to the line. The primaries 19,

89 and BI of cathode heating transformers 35, 43 and 61 are connected to the line in series.

When power is applied to the line I filamentary cathodes 33, 44, 45 and 68 are heated. Condenser 64 charges, the voltage regulator tube 60 ignites and relay contact 11 closes. A fixed voltage appears across control potentiometer 31. Current fiows through coil 40 of relay 4| so that contacts 52 and 16 are closed.

When the push-button 39 is operated contact 15 closes energizing relay 8 and starting the exposure. Condenser Zla now charges in accordance with the amount of charge traversing the X-ray tube. The voltage attained depends upon the capacity of condenser 21a and the ratio and degree of coupling of transformer 28a. The cathode 58 of control tube 22a is biassed an adjustable amount by the setting of control potentiometer 31. When the voltage of condenser 2la attains a value equal to the difference between the ignition voltage of tube 22a and the bias voltage from the control potentiometer 31, tube 221: ignites. This causes a marked lowering of the potential of the grids 56 and 51 of tubes 46 and 41 resulting in an interruption in the fiow of current through the coil 40 of relay 4|. The resulting opening of contact 15 de-energizes relay 8 and terminates the exposure. When the discharge through tube 22a ends the grids 56 and 51 no longer block the fiow of current through tubes 46 and 41. A spontaneous repetition of the exposure does not, however, occur because at this stage contacts 52 and 53 are both open, preventing closure of relay 4|. When the pushbutton 39 is again released, relay 4| does close but now relay 8 is not energized because contact 15 is open. Release of push-button 39 also causes the discharge of condenser 2| a through resistance 36 and contact 38, thus resetting the entire device for the next exposure. Relay 1| serves to prevent an exposure unless regulator tube 60 is receiving its normal current. The arrangement of heating transformers 35, 43 and 61 with primaries 19, 80 and 8| in series serves to prevent an exposure in the event of failure of heating current to any of the tubes.

The predetermination of the desired charge which shall traverse the X-ray tube during the exposure is accomplished by adjustment of the ratio of transformer 28a, adjustment of the coupling of said transformer, selection of the capacity of condenser Zia, adjustment of the control potentiometer 31 or any combination of these.

The device may be modified for use with multiphase X-ray generators. Each high tension winding may be tapped at its center to feed its own transformer rectifier system, corresponding to tube 26, transformer 28a, transformer 35 and the interconnection of these elements. The output of the multiplicity of such systems may be connected in parallel to a single timing condenser corresponding to condenser Zia.

The device may also be used with constant potential and voltage multiplying systems. In fact it may be applied to any generator in which the current to be controlled. S-peridic and of a wave form such that the transformer 28a will operate satisfactorily. The condition for such satisfactory operation in which the charge delivered to the condenser 2 la bears a fixed relation to the absolute sum of the charges passing through the primary of the transformer winding 29a is that the currentthrough this primary winding,

denoted by the symbol 1', shall satisfy either of the following relations:

where t is the time at which the current has the value 1', T is the period and the integrations are carried over a complete cycle.

The control of the power circuit may be carried out by means of'electronic tubes instead of relays without affecting the spirit of the invention and the scope of the appended claims.

The foregoing description and accompanying drawings are given by way of example only and any modification within the scope of the appended claims may be resorted to without departing from the spirit of the invention.

I claim:

1. Apparatus for timing X-ray exposures in conjunction with an X-ray tube and a high-tension transformer comprising a low-tension transformer, onewinding thereof being connected in the secondary circuit of the high-tension transformer, a rectifier, a condenser, said condenser being fed by the other winding of said low-tension transformer through said rectifier, a control tube responding to the voltage of said condenser, and means by which said control tube operates to terminate the X-ray exposure when a predetermined selected amount of electric charge has traversed the X-ray tube.

2. Apparatus as claimed in claim 1, wherein means are provided for preventing a spontaneous repetition of exposure after termination.

3. Apparatus as claimed in claim 1, wherein means are provided for discharging the condenser after the exposure.

4. Apparatus as claimed in claim 1, wherein the turns ratio of the transformer is adjustable to predetermine the charge which shall traverse the condenser durin the exposure.

5. Apparatus as claimed in claim 1, wherein thecoupling between the windings of the transformer is adjustable to predetermine the charge which shall traverse the condenser during the exposure.

6. Apparatus as claimed in claim 1, wherein a control potentiometer is provided for predetermining the charge which shall traverse the condenser by adjustment thereof, said potentiometer being supplied by a power supply system, and said potentiometer being connected to affect the potential of an electrode of the control tube.

'7. Apparatus as claimed in claim 1, wherein a control potentiometer is provided for predetermining the charge which shall traverse the condenser by adjustment thereof, said potentiometer being supplied by a power supply system including a regulator tube of the gas discharge type, said potentiometer being connected to affect the potential of an electrode of the control tube, and

wherein means are provided to prevent the possibility of an exposure if said voltage regulator tube is not receiving the normal current therefor.

8. Apparatus as claimed in claim 1 including a control tube, rectifier tubes and amplifier tubes in which at least two of said tubes are provided with heated cathodes, wherein separate transformers are used for heating said cathodes and wherein the primaries of a plurality of said separate transformers are connected in series.

MYRON M. SCHWARZSCHILD. 

